Influence of skin tension and formalin fixation on sonographic measurement of tumor thickness.

Background: High-resolution sonographic measurement of skin tumors, especially of malignant melanomas, allows presurgical assessment of the most important prognostic factor--tumor thickness. A good correlation between ultrasonographic and histopathologic thickness measurement has been reported. Procedures for preparing tissue for histopathologic examination, such as excision, fixation in formalin, dehydration in alcohol, and embedding in paraffin, may cause the tissue to retract and shrink and may therefore affect thickness measurement results.
Objective: Our purpose was to evaluate the influence of skin preparation procedures on ultrasound measurement results and to compare tumor thickness values obtained sonographically versus those obtained histopathologically.
Methods: Sixty-three epithelial (n = 37) and melanocytic (n = 26) tumors, benign as well as malignant, were measured by ultrasound before and immediately after excision and after overnight fixation. Sonographically and histopathologically determined tumor thicknesses were compared.
Results: Loss of skin tension after excision led to an increase in measured tumor thickness because of spherical retraction of the specimen. Subsequent fixation, dehydration, and embedding reversed this effect, so that altogether, histopathologically assessed tumor thickness was only slightly lower than ultrasound-derived thickness before excision. This was true for melanocytic as well as epithelial lesions.
Conclusion: Loss of skin tension after excision and tissue preparation procedures seem to offset each other and lead to a good overall correlation between ultrasonographic and histopathologic measurements.